The present invention relates to a transceiver unit comprising:                a receiver unit adapted to detect from a physical medium a first downstream handshake initiation signal and a first upstream handshake initiation signal,        a transmitter unit adapted to transmit over said physical medium a second upstream handshake initiation signal,        a self identification module adapted to identify said transceiver unit as a central unit or as a remote unit.        
Such a transceiver unit is already known in the art, e.g. from the recommendation entitled “Handshake Procedures for Digital Subscriber Line (DSL) Transceivers”, reference G.994.1, pre-published by the International Telecommunication Union (ITU) on February 2001.
This recommendation provides a flexible mechanism for Digital Subscriber Line (xDSL) transceivers to exchange capabilities and to select a common mode of operation. This is known as the handshake procedure. With respect to the handshake procedure, a transceiver unit is referred to as an HandShake Termination Unit (HSTU).
A transceiver unit sited at a Central location (e.g., a central office) is referred to as a HSTU-C. A transceiver unit sited at a Remote location (e.g., customer premises) is referred to as a HSTU-R. Downstream refers to signals flowing from the central unit to the remote unit, upstream refers to signals flowing from the remote unit to the central unit.
The handshake procedure begins with the transmission and detection of specific handshake initiation and confirmation signals, the composition and the timing of which being specified in §11.1 (p. 78-79) for duplex mode of operation, and in §11.2 (p. 79-80) for half-duplex mode of operation.
Transmit and receive spectra, signal composition and timing, state transition diagram, etc, are different for a central unit and a remote unit. A transceiver unit shall thus identify itself as a central unit or (exclusive) as a remote unit prior to the beginning of the handshake procedure. This is usually achieved by means of hardly/softly configured data, e.g. by reading from a specific location in memory the type of housing equipment wherein the transceiver unit is embedded.
The prior art solution requires careful equipment selection and/or manual equipment configuration. This solution is even more tedious if a network element shall operate in some respects as a central unit, and in other respects as a remote unit, e.g. an access concentrator at an intermediate hierarchical level.